1. Field of the Invention
The present invention relates to an acid generator, sulfonic acid, sulfonic acid derivative, and radiation-sensitive resin composition. More particularly, the present invention relates to a photoacid generator suitable for use in a radiation-sensitive resin composition which is used as a chemically amplified resist for microfabrication utilizing various types of radiation, for example, deep ultraviolet rays such as a KrF excimer laser, ArF excimer laser, F2 excimer laser, or EUV (extreme ultraviolet), X-rays such as synchrotron radiation, or charged particle rays such as electron beams, to a sulfonic acid generated from said acid generator, a sulfonic acid derivative useful as a raw material or intermediate for synthesizing said acid generator, and a positive-tone or negative-tone radiation-sensitive resin composition containing said acid generator.
2. Description of the Background Art
In the field of microfabrication represented by fabrication of integrated circuit devices, a lithographic technology enabling microfabrication with a line width of 0.20 μm or less has been demanded in order to achieve higher integration.
A conventional lithographic process utilizes near ultraviolet rays such as i-line radiation. It is known in the art that microfabrication with a line width of a sub-quarter micron order using near ultraviolet rays is very difficult.
Therefore, use of radiation with a shorter wavelength has been studied for enabling microfabrication with a line width of 0.20 μm or less. As radiation with a shorter wavelength, deep ultraviolet rays represented by a line spectrum of a mercury lamp and an excimer laser, X-rays, electron beams, and the like can be given. Of these, a KrF excimer laser (wavelength: 248 nm), an ArF excimer laser (wavelength: 193 nm), an F2 excimer laser (wavelength: 157 nm), EUV (wavelength 13 nm), and electron beams have attracted attention.
As a radiation-sensitive resin composition applicable to shorter wavelength radiation, a number of compositions utilizing a chemical amplification effect between a component having an acid-cleavable functional group and a photoacid generator which generates an acid upon irradiation (hereinafter called “exposure”) has been proposed. Such a composition is hereinafter called a chemically-amplified radiation-sensitive composition.
As the chemically-amplified radiation-sensitive composition, Japanese Patent Publication No. 27660/1990 discloses a composition comprising a polymer containing a t-butyl ester group of carboxylic acid or a t-butylcarbonate group of phenol and a photoacid generator. This composition utilizes the effect of the polymer to release a t-butyl ester group or t-butyl carbonate group by the action of an acid generated upon exposure to form an acidic group such as a carboxylic group or a phenolic hydroxyl group, which renders an exposed area on a resist coating readily soluble in an alkaline developer.
As characteristics demanded of a photoacid generator for a chemically-amplified radiation-sensitive composition, superior transparency to radiation, high quantum yield, and capability of producing an acid which has strong acidity, high boiling point, and a suitable diffusion distance in a resist coating (hereinafter referred as diffusion length) can be given.
To ensure high acidity, high boiling point, and appropriate diffusion length, the structure of an anionic moiety in the ionic photoacid generator and the structure of a sulfonyl moiety in the nonionic photoacid generator comprising a sulfonyl structure or a sulfonic acid ester structure are important. When the photoacid generator has a trifluoromethanesulfonyl structure, for example, even though a sufficiently strong acid to ensure adequate resolution performance of a photoresist is generated, there is a drawback of a high mask dependency due to the low boiling point and long diffusion length of the generated acid. When the photoacid generator has a sulfonyl structure with a large organic group such as a 10-camphorsulfonyl structure, even though the mask dependency is low due to the high boiling point and short diffusion length of the generated acid, the resolution performance as a photoresist is insufficient due to the poor acidity.
On the other hand, photoacid generators having a perfluoroalkylsulfonyl structure such as perfluoro-n-octane sulfonic acid (PFOS) have been given attention in recent years due to the adequate acidity, boiling point of the acid, and diffusion length.
However, viewing these photoacid generators having a PFOS-type perfluoroalkylsulfonyl structure from an environmental aspect, they have low combustibility and their bioaccumulation is suspected. A report issued by the U.S. Environmental Protection Agency, entitled “Perfluorooctyl Sulfonates; Proposed Significant New Use Rule” proposes regulating the use of these compounds. Therefore, in the field of microfabrication, the development of a component functioning excellently as a photoacid generator without these drawbacks has been desired.
The object of the present invention is to provide a novel photoacid generator which, when used as a photoacid generator sensitive to radiations or heat, exhibits high transparency to deep ultraviolet rays such as a KrF excimer laser, ArF excimer laser, F2 excimer laser, or EUV, and electron beams, exhibits comparatively high combustibility and no bioaccumulation, and produces an acid exhibiting high acidity, high boiling point, moderately short diffusion length in the resist coating, and low dependency to mask pattern density; a sulfonic acid generated from the photoacid generator; a sulfonic acid derivative useful as a raw material or intermediate for synthesizing the photoacid generator; and a positive-tone or negative-tone radiation-sensitive resin composition containing the photoacid generator.